This invention relates to an impact-absorbing sound-attenuating earcup assembly for use in a protective helmet or the like.
Earcup assemblies for attenuating ambient sound in noisy environments, such as in or around military helicopters or other aircraft, are well known in the art. Such assemblies are shown, for example, in Aileo U.S. Pat. Nos. 3,109,973, 3,470,564, 3,875,592 and 3,943,572, owned by the assignee herein. Currently available assemblies generally rely on the stiffness and surface density (i.e., mass per unit area) of the earcup to provide the desired sound attenuation. High stiffness and high surface density both decrease the amplitude of vibration of the earcup shell, thereby decreasing the noise inside the cup.
Current earcups provide good sound attenuation, but suffer from two limitations on their performance. First, in most lightweight aircraft helmets, the helmet is too small to avoid using the earcup as part of the crushing system that protects the head from impact. Most current cups are made with materials, thicknesses and shapes that make them too stiff to crush at low, nonlethal forces. Second, most commonly employed earcup materials are not well damped, and therefore resonance in the cup shell is not well controlled. Such resonances result in significant frequency-dependent drops in attenuation.